This research continues investigations of the motivational and performance effects of smoked marijuana under conditions in which drug administration is controlled by the experimenter and, as well, when it is controlled by each subject. Groups of three human subjects will live in a comfortable self-contained residential laboratory for 15-28 days. Their behavior will be observed and recorded, and access to all activities and to the other subjects will be programmed. Experimental procedures developed in the course of previous long-term research will be used to study motivation, cooperation, competition, and aggression. Subjects will be required to devote time to low-valued activities in order to earn access to their most valued activities. Previously reported research from this laboratory has indicated that under specific conditions, smoked marijuana interferes with the utilization of reinforcers. These findings suggest a change in motivation attributable to marijuana smoking, and further studies will attempt to delineate the conditions under which this possible "amotivational" effect occurs. In addition to evaluating the effects of marijuana upon individuals working for their own reinforcers, this research will investigate the effects of marijuana on functioning within a social group. In one experimental paradigm, subjects will continue to work in order to earn access to highly preferred activities, but will have the opportunity to engage in cooperative and/or competitive strategies to manage and control individual and group resources. Additional experiments will extend this cooperation-competition paradigm under behaviorally stressful conditions as a means of evaluating the effects of marijuana on aggressive behavior. These studies will extend the generality of the research being carried out on the behavioral effects of marijuana to include social behavior. This is an important area of investigation since it is the context in which most marijuana self-administration occurs.